When the rotor disk is tilted, the thrust vector tilts as well. Thrust is the force along the rotor axis, so tilting the disk creates a vertical component that helps lift and a horizontal component that pushes the aircraft forward. In level forward flight, the horizontal component is what provides thrust in the forward direction, while the vertical component continues to balance weight as lift. So the horizontal part of the tilted thrust vector is the thrust, and the vertical part is lift.

Airfoils are most commonly classified by camber. There are two broad categories: symmetric, which has zero camber and identical curvature on top and bottom, and nonsymmetric or cambered, which has curvature that favors lift and is not identical on both sides. This distinction matters because cambered airfoils generate lift more readily and at smaller angles of attack, while symmetric airfoils rely more on the angle of attack to produce lift and have a neutral zero-lift angle. The option that lists both symmetric and cambered as the two basic types correctly captures this fundamental classification. The other choices point to either one type only or to a specific shape (elliptical) rather than the general categories by camber.

Countering rotor torque is about providing an opposite yawing moment so the fuselage doesn’t spin when the engine drives the main rotor. The classic solution is an anti-torque system—the tail rotor creates lateral thrust at the tail, producing a yaw moment that balances the torque produced by the main rotor. By adjusting how much thrust the tail rotor provides, you keep the helicopter’s heading in hover and control yaw throughout flight. Raising the main rotor blade pitch increases lift but also increases the torque the engine applies to the rotor; that doesn’t counter torque by itself, it actually changes how much anti-torque is needed. Downwash augmentation deals with airflow effects and doesn’t address torque reaction. Lateral cyclic input can influence motion and yaw only as a secondary effect, not as the primary method to counter torque.

In a semi-rigid rotor system, the hub provides a single flapping hinge, which allows the rotor disk to tilt as a unit. The mast is the fixed reference to the airframe, so the observable tilt of the rotor disk occurs relative to the mast. This arrangement lets the disk rotate its plane to balance lift differences between blades without requiring multiple hinges at the hub. The tilting is not described relative to the hub, blade root, or the aircraft’s centerline, but specifically relative to the mast.